In the technique for fabricating a liquid crystal panel in a thin film transistor liquid crystal display (TFT-LCD) industry, an alignment film is formed by printing an alignment liquid onto an array substrate and a color film substrate with an alignment film coating device. In the production process of a small size panel prior to the 8.5-generation line, during printing the alignment liquid, nitrogen is pressed into the alignment liquid, and a dispenser moves back and forth at both sides of an anilox roll to discharge an appropriate amount of alignment liquid, so that an appropriate amount of alignment liquid always exists on the anilox roll of the alignment film coating device, thus guaranteeing to printing the alignment film continuously. However, in the production process of the 8.5- or higher generation line, the coating of alignment liquid (e.g., polyimide PI solution) is generally performed by spraying, as shown in FIG. 1, in which droplets of alignment liquid are sprayed onto the array substrate and the color film substrate by a spraying device. The reason lies in the advantages of spraying. For example, the equipment is relatively simple, the thickness of alignment film can be adjusted during the production process, the switching period between products is short, the utilization efficiency of the alignment liquid is high, and there is no limitation regarding the products to be produced.
As the market competition is becoming fiercer, manufacturers of liquid crystal panels gradually produce high added-value products with a small size and high PPI (pixels per inch) in the 8.5-generation line to maximize their benefits. However, during productions of the products with a small size and high PPI, the flatness among pixels on the substrate is relatively poor, PI diffuses in a smaller region within the same process time, which leads to non-uniform PI coating and diffusion. As a result, the finished product may suffer from PI-related mura, which degrades the display quality and decreases the price and profit. Besides, extending the process time or performing a secondary coating may decrease the yield and thus affect the economic benefit.